Severe engine vibration after warmed up

[TuffRR]

For those that don't know, i've just put back together the 4.4 in my Rover. I've had a few fueling issues which seem to have sorted themselves out for the time being. (i'm running 3.5 injection ATM).

On startup the motor feels nice and smooth with no vibrations. After about two minutes of running though, a severe vibration starts that gradually gets worse. It feels the worst around 2000rpm and is not so noticeable below. I rotated the torque converter 180 degrees last night to see if this had any effect but it didn't. Its not the driveshafts because it happens in neutral when i rev the motor as well. The vibration does not seem to be affecting the performance as the motors running fine (if only a little underfueled).

The fact that it starts to happen only when warmed up has got me stumped. What could be causing this?

[TuffRR]

Update: Have narrowed it down to the torque converter or flex plate. When we fired it up for the first time we were unaware that the bellhousing bolts were not in (workshop that previously had the car failed to mention this bit )

This caused the bellhousing to seperate from the block a little which would have caused the flex plate or torque converter to deform. It would be more likely that it bent the flex plate but if this was the case, the vibrations would be there from startup. This leaves the TC which does go through changes as it warms up (oil thins). I'm not sure exactly what happened to the TC but this seems to be the best explanation. I still have drive to the wheels to it didn't completely destroy it.

[DamTriton]

An educated guess would be a spark plug that has its gap set too wide, or a dud plug, and threrfore failing to spark when the ECU goes from open loop (rich, "cold start") to closed loop operation (leaner, controlled by O2 sensor feedback) This would explain the 2 mins or so of good running (firing on all cyls) followed by the missing. In light of the use of the 3.5 EFI this overlean mixture could be due to the limits on the OE settings of the ECU.


There again, what would I know? I'm only a Kia Sportage owner

[Macca177]

could be off.... but have ya checked ya engine mounts...most engine vibrations are usally a dud engine mount...worth a look anyways

[Roktruk]

How 'bout the fan? RR's have a habit of shedding fan blades, and since it's a funny offset design anyway a cracked blade will cause a wobble.

[TuffRR]

Engine mounts are in good nick so i doubt this is the problem.

I'm sceptical that its a spark problem because if it was firing on only seven cylinders, the performance would not be as good as it is.